Materials stored in containers frequently have both a liquid phase and a gas phase. With materials such as hazardous materials, it is frequently desirable to allow gas phases to vent while retaining liquid phases in the container.
An example of such hazardous materials is plutonium in aqueous hydrochloric acid or nitric acid solutions. As pipes and tanks containing these solutions are drained, they are generally drained into 1 gallon, high density, polyethylene bottles with polypropylene caps for interim storage until permanent solidification or immobilization may be conducted. The solutions contain as much as 140 g/l of plutonium which has the radiolytic effect of generating hydrogen gas. Hydrogen gas in the bottles accelerates embrittlement of the bottles which, over time, can lead to failure of the bottles. Since plutonium is considered to be highly carcinogenic, leak-age of plutonium into the environment surrounding the bottles poses a danger which must be avoided. Typically, venting of these bottles is through a GOR-TEX® element in the polypropylene cap. GOR-TEX® is impervious to liquids but pervious to gases. It has proven difficult to select an adhesive for securing the GOR-TEX® material to the caps because many adhesives tend to degrade in the presence of aqueous hydrochloric and nitric acid solutions containing plutonium.
This concern arises with respect to other structures such as the filter assembly disclosed in U.S. Pat. No. 4,957,518 in which a GOR-TEX®, liquid permeable, but gas impermeable, barrier is employed. In this patent, the GOR-TEX® barrier may be held in place either mechanically or by an adhesive. Mechanical retention relies on clamping the GOR-TEX® barrier between two surfaces. Clamping can be unreliable. The other approach is, of course, to use adhesive, but, as previously stated, adhesive may be attacked by the material stored in the containers. In addition, there are fabrication problems which arise when using adhesive. This is because if a perforated substrate is used to support the GOR-TEX® barrier, the adhesive may flow over into and seal at least some or not all of the perforations.
In view of the aforementioned problems, as well as other problems, there is a need for new and improved vent structures; a need for a method for fabricating such structures; and a need for vent configurations employing the advantages offered by the improved vents.